In recent years, techniques for polishing electronic parts such as semiconductor substrates to a higher accuracy have been necessary with the development of electronics industry itself.
As shown in FIG. 5, in a known method of polishing a semiconductor substrate or the like into a smooth, uniform thickness, a polyurethane pad attached to bottom end of a polishing rod 2 disposed above the work 1, which is covered by a colloidal silica solution, is moved into contact with the surface of the work 1, and the polishing rod 2 while autorotating about its central axis, successively horizontally displaced while reciprocating relatively on the work 1.
Polishing of the work 1 is achieved by previously measuring the thickness for each of the portions of the work 1 and controlling the autorotating speed of the polishing rod 2, the polishing pressure against the work, and the retaining time or the like corresponding to the required polishing amount for each of the portions. In this case, since the surface area of the work that can be polished by one polishing rod 2 is small, a plurality of polishing rods 2 are usually disposed in a desired arrangement density relative to the surface of the work 1 to be polished.
However, with the polishing device of the aforementioned type, since the polishing rod 2 is disposed vertically to the surface of the work 1 to be polished, the bottom end of the polishing rod 2 is formed as a flat surface in parallel with the polished surface and the polishing rod 2 autorotates with no rotation of the work 1, the relative speed of the polishing rod 2 to the work 1 is a maximum at the outer circumference and reduces to zero in the central portion at the bottom end of the polishing rod 2. Therefore, in the surface of the work 1 to be polished, only the portion at the peripheral edge of polishing rod 2 is well polished while the polishing amount is smaller at a portion near the central portion of the polishing rod 2, and such portion remains in a raised form. Generally, since the surface of the work 1 before polishing is in an uneven roughened surface, the above-mentioned trend is remarkable particularly upon polishing a convex portion, making it difficult to polish the entire surface of the work 1 to a uniform thickness.
Further, the polishing rod 2 is sometimes set to be inclined relative to the surface of the work 1 to be polished. In such a case, the polished surface is polished asymmetrically.
In order to eliminate the drawback of the polishing device wherein the polishing rod 2 autorotates solely, a planetary polishing device has been developed wherein a polishing rod 2 is caused to revolve along the surface to be polished under autorotation, which can overcome the problem that polishing is conducted extremely only at the outer edge of the polishing rod 2 as described above.
However, with the planetary type polishing device, since the mechanism for driving the polishing rod 2 is complicated in structure and is enlarged in size, a plurality of polishing rods cannot be disposed in a high density relative to the surface of the work 1 to be polished and a satisfactory polishing efficiency cannot be obtained. Further, the device can neither resolve the problem of the asymmetric polishing if the polishing rod 2 is inclined relative to the surface to be polished.
Furthermore, in the above-mentioned polishing rod autorotation type polishing device, the speed of the polishing fabrication is determined by the rotational linear velocity along the outermost edge at the bottom end of the polishing rod under autorotation. If the pressure of contact at the outermost edge is lowered, since the efficiency for the polishing fabrication is lowered, a sufficiently large load has to be applied to the polishing rod 2 as far as the outermost edge. However, when a high pressure is applied to the outermost edge of the polishing rod 2, since the surface of the work 1 to be polished undergoes a strong shearing Stress at the inside and the outside of the outermost edge of the polishing rod 2, there is a worry that a fatal defect will be created in the crystal surface of the work if it is, for example, a single crystal silicon substrate.
It is an object of the present invention to overcome the foregoing problems in the conventional method of polishing a semiconductor substrate or the like and to provide a novel polishing method capable of efficiently polishing a work at a more uniform thickness than usual while avoiding fatal defects in the crystal surface of the substrate after polishing. The object is also to provide a polishing device using such a method.